Painting bought for 50 at auction worth 388,000--A postcard-sized landscape painting bought as part of a box of trinkets costing $50 at auction has been valued at almost $400,000.

The 19th-century artwork was picked up 10 years ago by retired consultant ophthalmic surgeon Robin Darvell after he spotted a faint signature on the frame.

It depicts a landscape in summer with trees in the foreground and rolling hills in the background, set against a blue sky with a few white, fluffy clouds.

The painting had been kept in a drawer but was recently discovered hidden with some paperwork.

Darvell's son Robert, 45, approached Curtis Dowling, the host of CNBC’s "Treasure Detectives", for an appraisal. Dowling confirmed it was an original by British painter John Constable.Dowling believes that the painting once belonged to Constable’s father-in-law Charles Bicknell and valued the painting at $388,000.

"These things are out there in someone's cupboard or shed or hanging on their wall," Dowling said. "But they don't know what they have. As people age they have all these things and we make the assumption that everyone knows these artists. In America, there is probably billions of dollars artwork or other antiques that people are sitting on without knowing it."

Famous for his landscape paintings, Constable is best known for “The Hay Wain”, which hangs in England's National Gallery.His painting “The Lock,” which had been housed in Madrid’s Bornemisza Museum, sold at Christie’s for £22.4 million ($35 million) last year.

Robert Darvell said he was still in a state of shock by the news, adding that he now plans to show the previously unseen painting to the public.

He said that when his father had suggested that it was a genuine Constable, his family had rolled their eyes and laughed with him.

“We never took him seriously,” he said. “I don’t think he believed it entirely, so it became a bit of a family joke.”